fresh labels for perishable products

a new method of tracking a foods expiration date by using a universally recognizable visual. the label has one layer of info for the food with the barcode, and another on top with special ink reactive to ammonia. the ink is made of nontoxic, safe pigment of purple cabbages. the new design keeps people honest by changing colors based on the level of ammonia the food emits as it ages. once the meat or other perishable product is past it&rsquos due, the label will have turned from white to blue, making the item unscannable. after it has passed its expiration date the barcode is no longer readable, making it impossible to sell.